CPU Caching Problems

OK so I have been working on this HP Compaq business dc5000 Small Form Factor for some time now, I have updated the BIOS, Intel P4 Chipset, replaced the hard drive (Not related) and replaced the CPU itself from a 2.80GHz P4 to a 3.0GHz P4 of the same spec other then speed. But the system STILL cant cache. An earlier post here on MDL I was told it was possibly the CPU that was bad. But after replacing it, it still has the same result. I swapped the HDD with one loaded with XP (The systems native OS) mainly because I can crash it without damage like Win 7. Any suggestions as to what this problem could be? I have looked up every possible solution and I cant find the cause...

I do have one last trick to try before I give up on this piece of trash. I'm going to try (just for s**ts and grins) a different graphics card, overriding the Integrated graphics processor. The errors I'm getting just might be the graphics causing my problem.